In the electron transport system responsible for the oxidative phosphorylation for synthesis of ATP in mitochondria, mainly four types of protein complexes are involved, and are called as complexes I, II, III and IV (Kozo Utsumi and Masayasu Inoue, Ed. “New Mitochondriology” pages 8-13; Takashi Kanamori and Shigeo Ohta, “Electron Transport System and Energy Converting SyStem”, Kyoritsu Shuppan. 2001). For these complexes, i.e. the complex I (NADH-ubiquinone oxidoreductase), the complex III (ubiquinol-cytochrome c oxidoreductase), and the complex IV (cytochrome c oxidoreductase), superior inhibitors have been known and are used in the biochemical studies (Kozo Utsumi and Masayasu Inoue, Ed. “New Mitochondriology”, pages 424-426; Kozo Utsumi, “List of inhibitors used for studies on energy transduction of mitochondria”, Kyoritsu Shuppan, 2001).
With regard to the complex II (succinate-ubiquinone oxidoreductase) inhibitor, thenoyltrifluoroacetone, etc. has been frequently used, however its inhibitory concentration was very weak such as in the order of iM (The Japanese Biochemical Society, Ed., Experimental Biochemistry, No. 12, “Energy Metabolism and Biological oxidation” (Upper volume) pages, 215-255; Yasuo Kagawa and Akira Asano, “Preparative Methods for Mitochondria and Compositional Components, Tokyo Kagaku Dozin, 1976). Further, carboxins have been said to have strongest inhibitory activity among the prior known complex II inhibitors (P. C. Mowery, B. A. C. Ackrell and T. P. Singer, Biochem. Biophys. Res. Commun., 71, 354-361, 1976), however, it was considerably weak activity as compared with rotenone, a complex I inhibitor, and antimycin, a complex III inhibitor (The Japanese Biochemical Society, Ed. Experimental Biochemistry, No. 12, “Energy Metabolism and Biological Oxidation” (Upper volume) pages, 215-255; Yasuo Kagawa and Akira Asano, “Preparative Methods for Mitochondria and Compositional Components, Tokyo Kagaku Dozin, 1976).